Post-foaming or self-foaming shave gels are now well-known and have been described, for example, in U.S. Pat. Nos. 2,995,521 (Bluard), 3,541,581 (Monson), 4,405,489 (Sisbarro), 4,528, 111 (Su), 4,651,503 (Anderson), 5,248,495 (Patterson), 5,308,643 (Osipow), and 5,326,556 (Barnet) and published PCT application WO 91/07943 (Chaudhuri). Such compositions generally take the form of an oil-in-water emulsion in which the self-foaming agent, generally a volatile (i.e. low boiling point) aliphatic hydrocarbon, is solubilized in the oil phase, and the water phase comprises a water-soluble soap component. The product is generally packaged in an aerosol container with a barrier, such as a piston or collapsible bag, to separate the self-foaming gel from the propellant required for expulsion of the product. The product is dispensed as a clear, translucent or opaque gel that is substantially free from foaming until it is spread over the skin, at which time it produces a foam lather generated by the volatilization of the volatile hydrocarbon foaming agent.
While the conventional self-foaming shave gels have gained wide acceptance by consumers, they can be somewhat harsh and drying to the skin due to the soap component. To counteract this effect, the typical shave gel composition is formulated with skin soothing components such as humectants, emollients, silicones, etc. While the addition of such components substantially improve the aesthetics of the product, repeated use can still produce undesirable drying of the skin, particularly among female users. Accordingly, it is highly desirable to develop a self-foaming shave gel composition that is less harsh and drying to the skin than conventional shave gels, without sacrificing any of the performance characteristics thereof.
N-acyl sarcosinates are well-known anionic surfactants represented by the formula ##STR1## where R is a fatty acid hydrocarbon chain. These materials are typically used in the form of water-soluble salts formed by neutralization with sodium, potassium or ammonium hydroxide or triethanolamine and have been suggested for use in a wide variety of products including shampoos, detergents, dentifrices, hand soaps, and shave creams. For example, aerosol shaving creams containing sarcosinates are disclosed in U.S. Pat. Nos. 3,959,160 (Horsler), 4, 113,643 Thompson), and 4,140,648 (Thompson) and in Harry's Cosmeticology (7th ed., 1982), p. 169 (see Croda Cosmetic and Pharmaceutical Formulary Supplement, formula SV11 ). A soap-free non-aerosol shave cream which may optionally contain a sarcosinate is disclosed in U.S. Pat. No. 4,892,729 (Cavazza) and a non-aerosol shave gel which contains both a soap and a sarcosinate is disclosed in U.S. Pat. No. 5,340,571 (Grace).
Soap-free shaving products are also known, but have met with limited acceptance. For example, U.S. Pat. Nos. 4,046,874 (Gabby) and 4,761,279 (Khalil) disclose shaving cream compositions containing respectively a polyglycerol fatty ester (e.g. triglycerol monostearate) and a fatty ester of lactylic acid (e.g. sodium salt of stearyl lactylic acid). A pre-shave gel containing polyethylene oxide polymer and polysulfonic acid polymer is disclosed in U.S. Pat. No. 4,999,183 (Mackles).